OK, let's work through this together. We're starting with 286 and we're going to multiply it by 42, which means we add 286 to itself 42 times.
Step 1: 0 + 286 = 286
Step 2: 286 + 286 = 572
Step 3: 572 + 286 = 858
Step 4: 858 + 286 = 1144
Step 5: 1144 + 286 = 1430
Step 6: 1430 + 286 = 1716
Step 7: 1716 + 286 = 2002
Step 8: 2002 + 286 = 2288
Step 9: 2288 + 286 = 2574
Step 10: 2574 + 286 = 2860
Step 11: 2860 + 286 = 3146
Step 12: 3146 + 286 = 3432
Step 13: 3432 + 286 = 3718
Step 14: 3718 + 286 = 4004
Step 15: 4004 + 286 = 4290
Step 16: 4290 + 286 = 4576
Step 17: 4576 + 286 = 4862
Step 18: 4862 + 286 = 5148
Step 19: 5148 + 286 = 5434
Step 20: 5434 + 286 = 5720
Step 21: 5720 + 286 = 6006
Step 22: 6006 + 286 = 6292
Step 23: 6292 + 286 = 6578
Step 24: 6578 + 286 = 6864
Step 25: 6864 + 286 = 7150
Step 26: 7150 + 286 = 7436
Step 27: 7436 + 286 = 7722
Step 28: 7722 + 286 = 8008
Step 29: 8008 + 286 = 8294
Step 30: 8294 + 286 = 8580
Step 31: 8580 + 286 = 8866
Step 32: 8866 + 286 = 9152
Step 33: 9152 + 286 = 9438
Step 34: 9438 + 286 = 9724
Step 35: 9724 + 286 = 10010
Step 36: 10010 + 286 = 10296
Step 37: 10296 + 286 = 10582
Step 38: 10582 + 286 = 10868
Step 39: 10868 + 286 = 11154
Step 40: 11154 + 286 = 11440
Step 41: 11440 + 286 = 11726
Step 42: 11726 + 286 = 12012

So, 286*42 = 12012